This invention relates to a rotational direction detecting apparatus for a three-phase brushless DC (i.e., direct-current) motor.
A three-phase brushless DC motor is simple in mechanical structure and excellent in controllability and is therefore preferably used in the CPU controls performed in numerous motor driven apparatuses such as a motor-driven power steering device. According to this kind of three-phase brushless DC motor used for various CPU controls, it is desirable to promptly detect any malfunction or failure of CPU when it occurs.
To satisfy such a desire, the Japanese Patent Application Laid-open No. 13-018819(2001) proposes providing a sub CPU which monitors the performance of a main CPU used for controlling a three-phase brushless DC motor. However, according to this prior art, the circuit arrangement and the software used for a control system tend to be complicated due to necessity of incorporating a plurality of CPUs into this control system.
Furthermore, compared with an ordinary hardware logic circuit, the CPU is weak against electromagnetic noises and accordingly has the tendency of causing malfunctions and failures at higher probabilities. Thus, when a monitoring CPU is additionally provided, it is then necessary to provide an effective countermeasure for preventing the failure of this kind of sub CPU.